The present invention concerns implantable medical devices, such as defibrillators and cardioverters, particularly structures and methods for capacitors in such devices.
Capacitors have undergone substantial improvement over the years. Smaller capacitors are in demand for various applications. One such application is for biomedical implants. For example, defibrillators and pacemakers use capacitors for pulse delivery.
The defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing into the walls of a heart after implantation. Within the housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering bursts of electric current through the leads to the heart.
The capacitor can take the form of a flat aluminum electrolytic capacitor. Flat capacitors include a stack of flat capacitor elements mounted within a capacitor case. Each flat capacitor element includes one or more separators between two sheets of aluminum foil. One of the aluminum foils serves as a cathode (negative) foil, and the other serves as an anode (positive) foil. The capacitor elements each have an individual capacitance (or energy-storage capacity) proportional to the surface area of the foil.
One drawback in manufacturing such capacitors is that each of the anodes and each of the cathodes must be connected together. For instance, all the anodes are crimped or welded together and attached to a feedthrough terminal for connection to circuitry outside the capacitor case. Another process is also done for the cathode foils in the capacitor stack. Errors during the manufacturing steps may cause defects in the capacitor or decrease the reliability of the capacitor after it is constructed. Another drawback is that the interconnections take up space within the capacitor. This increases the size of the capacitor, which is undesirable when the capacitors are used for implantable medical devices such as defibrillators.
Thus, what is needed is a simple way to provide the anode and cathode interconnections of capacitors with as few steps as possible and which lends itself to mass producing said capacitors.
To address these and other needs, interconnection structures and methods for flat capacitors have been devised. In one embodiment, a method includes connecting together one or more anode connection members of one or more anode foils and one or more cathode connection members of one or more cathode foils and electrically isolating the one or more anode foils from the one or more cathode foils. Among other advantages, the method reduces the processing steps for interconnecting the foils of a capacitor, and provides a capacitor having a smaller amount of room taken up by its interconnections.
In one aspect, a capacitor having a first anode layer, a second anode layer, a cathode layer between the first anode layer and the second anode layer, a first separator layer between the first anode layer and the cathode layer, a second separator layer between the second anode layer and the cathode layer; and a conductive interconnect between the first anode layer and the second anode layer, the conductive interconnect passing through a cathode hole in the cathode; wherein the conductive interconnect has a cross section which is smaller than the cathode hole and the conductive interconnect is placed to avoid direct electrical contact with the cathode layer and wherein the first anode and the second anode are electrically connected through the conductive interconnect.
Another aspect of the present invention includes various implantable medical devices, such as pacemakers, defibrillators, and cardioverters, incorporating one or more capacitors having one or more of the novel features described above.